FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the existing UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a LTE (Long-Term Evolution) system.
The E-UMTS network can roughly be divided into an E-UTRAN and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), an Access Gateway (AG) that is located at an end of the E-UMTS network and connects with one or more external networks. The AG may be divided into a part for processing user traffic and a part for handling control traffic. Here, an AG for processing new user traffic and an AG for processing control traffic can be communicated with each other by using a new interface. One eNode B may have one or more cells. An interface for transmitting the user traffic or the control traffic may be used among the eNode Bs. The CN may comprise an AG, nodes for user registration of other UEs, and the like. An interface may be used to distinguish the E-UTRAN and the CN from each other.
The various layers of the radio interface protocol between the mobile terminal and the network may be divided into a layer 1 (L1), a layer 2 (L2) and a layer 3 (L3), based upon the lower three layers of the Open System Interconnection (OSI) standard model that is well-known in the field of communications systems. Among these layers, Layer 1 (L1), namely, the physical layer, provides an information transfer service to an upper layer by using a physical channel, while a Radio Resource Control (RRC) layer located in the lowermost portion of the Layer 3 (L3) performs the function of controlling radio resources between the terminal and the network. To do so, the RRC layer exchanges RRC messages between the terminal and the network. The RRC layer may be located by being distributed in network nodes such as the eNode B, the AG, and the like, or may be located only in the eNode B or the AG.
FIG. 2 shows exemplary control plane architecture of a radio interface protocol between a terminal and a UTRAN (UMTS Terrestrial Radio Access Network) according to the 3GPP radio access network standard. The radio interface protocol as shown in FIG. 2 is horizontally comprised of a physical layer, a data link layer, and a network layer, and vertically comprised of a user plane for transmitting user data and a control plane for transferring control signaling. The protocol layer in FIG. 2 may be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based upon the lower three layers of the Open System Interconnection (OSI) standards model that is widely known in the field of communication systems.
Hereinafter, particular layers of the radio protocol control plane of FIG. 2 and of the radio protocol user plane of FIG. 3 will be described below.
The physical layer (Layer 1) uses a physical channel to provide an information transfer service to a higher layer. The physical layer is connected with a medium access control (MAC) layer located thereabove via a transport channel, and data is transferred between the physical layer and the MAC layer via the transport channel. Also, between respectively different physical layers, namely, between the respective physical layers of the transmitting side (transmitter) and the receiving side (receiver), data is transferred via a physical channel.
The Medium Access Control (MAC) layer of Layer 2 provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of Layer 2 supports the transmission of data with reliability. It should be noted that if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself may not need to exist. The PDCP layer of Layer 2 performs a header compression function that reduces unnecessary control information such that data being transmitted by employing Internet Protocol (IP) packets, such as IPv4 or IPv6, can be efficiently sent over a radio interface that has a relatively small bandwidth.
The Radio Resource Control (RRC) layer located at the lowermost portion of Layer 3 is only defined in the control plane, and handles the control of logical channels, transport channels, and physical channels with respect to the configuration, reconfiguration and release of radio bearers (RB). Here, the RB refers to a service that is provided by Layer 2 for data transfer between the mobile terminal and the UTRAN.
As for channels used in downlink transmission for transmitting data from the network to the mobile terminal, there is a Broadcast Channel (BCH) used for transmitting system information, and a downlink Shared Channel (SCH) used for transmitting user traffic or control messages. A downlink multicast, traffic of broadcast service or control messages may be transmitted via the downlink SCH or via a separate downlink Multicast Channel (MCH). As for channels used in uplink transmission for transmitting data from the mobile terminal to the network, there is a Random Access Channel (RACH) used for transmitting an initial control message, and an uplink Shared Channel (SCH) used for transmitting user traffic or control messages.
As for downlink physical channels for transmitting information transferred via the channels used in downlink transmission over a radio interface between the network and the terminal, there is a Physical Broadcast Channel (PBCH) for transmitting BCH information, a Physical Multicast Channel (PMCH) for transmitting MCH information, a Physical Downlink Shared Channel (PDSCH) for transmitting PCH and a downlink SCH information, and a Physical Downlink Control Channel (PDCCH) (also, referred to as ‘DL L1/L2 control channel’) for transmitting control information provided by the first and second layers such as a DL/UL Scheduling Grant, and the like. As for uplink physical channels for transmitting information transferred via the channels used in uplink transmission over a radio interface between the network and the terminal, there is a Physical Uplink Shared Channel (PUSCH) for transmitting uplink SCH information, a Physical Random Access Channel (PRACH) for transmitting RACH information, and a Physical Uplink Control Channel (PUCCH) for transmitting control information provided by the first and second layers, such as a HARQ ACK or NACK, a Scheduling Request (SR), a Channel Quality Indicator (CQI) report, and the like.
Description of a procedure for an uplink time synchronization alignment in a related art LTE system will be given. In the related art LTE system, the time synchronization of uplink must be aligned in order to minimize interferences between terminals. Therefore, to align the uplink time Sync, a base station (or network) calculates a time Sync alignment value based on certain control signals transmitted from a terminal, transmits the calculated time Sync alignment value to the terminal, and then the terminal applies such time Sync alignment value for uplink time alignment. More specifically, the base station calculates a time Sync alignment value of a terminal using a random access preamble or Sounding Reference Symbols (SRS) transmitted from the terminal. After the calculation, the base station transmits the calculated time Sync alignment value whenever it is necessary. After the time Sync alignment value is received by the terminal, the terminal then applies the time Sync alignment value, and starts or restarts a timer for the time Sync. It is assumed that the uplink synchronization is considered to be maintained until the expiration of the started or restarted timer, and the terminal can not transmit any other data or control signal to the uplink except a transmission of random access preamble after the timer is expired. Generally, the terminal has to request a radio resource to the base station when the radio resource is necessary for the uplink transmission. Here, if the terminal has a PUCCH (Physical Uplink Control Channel) assigned from the base station for a transmission of Scheduling Request (SR), the terminal can request the radio resource through the PUCCH. After such request from the terminal, the base station can allocate adequate radio resource to the terminal, and the terminal can transmit an uplink data using the allocated radio resource.
However, this is some case that a transmission of uplink data using the allocated radio resource is failed due to the expiration of the timer. For example, it is assumed that total time for the terminal to transmit the Scheduling Request (SR) to the base station through the PUCCH, to receive the allocated radio resource, and to transmit the uplink data using the allocated radio resource is 20 ms. Also, it is assumed that a remaining time from the transmission of the SR to the expiration of timer is 15 ms. In this case, if the terminal can not obtain a new time Sync alignment value for the next 15 ms from the base station, as described above, the terminal can not transmit any other data or control signal to the uplink except the random access preamble because the uplink synchronization is still considered to be maintained. Namely, as depicted in FIG. 4, the terminal transmits the Scheduling Request (SR) for a radio resource allocation to a base station at a time that the timer is still in operation. However, such SR transmission would be wasted at the time that the uplink data needs to be transmitted, as the uplink data can not be transmitted due to the expiration of the timer. Instead, the terminal has to perform a random access procedure for time synchronization. Such time waste or time delay due to the expiration of the timer would cause a great drawback in the related art.